Recent developments in the field of compressor design have also been concentrated on undersea arrangements of large compressors which are intended to be used for the pumping of natural gases.
Because of the particular operating conditions, in particular because of the greatly restricted accessibility both for maintenance purposes and by means of supply lines, the specialists are confronted with major requirements. The relevant environmental regulations forbid any exchange of substances between the equipment to be installed and the surrounding sea water. Furthermore, sea water is an aggressive medium and extreme pressure and temperature conditions can be found at the various depths in the sea. A further requirement is that the equipment should on the one hand have an extremely long life and on the other hand must be designed to be virtually free of maintenance. An additional exacerbating factor is not-inconsiderable contamination of the medium to be pumped which in some cases is chemically aggressive.
A compressor unit of the abovementioned type has already been disclosed in international patent application WO 02/099286 A1. With the aim of simplification, without any compromises, in order to reduce the maintenance effort, and of achieving a long life at the same time, this document proposes that the compressor rotor be formed integrally with the motor rotor and be mounted at each of the ends by means of just two radial bearings.
In addition, it is known from European patent application EP 1 074 746 B1 for a turbocompressor to be equipped with three radial bearings, with the motor rotor being connected to the compressor rotor by means of a coupling.
WO 2005/003512 A1 has already disclosed a compressor unit for under-sea compression, to which an automation unit is connected by means of special connectors which are suitable for under-sea use. In addition GB 370 003 A discloses the injection of an antifreeze during the compression of air.
The compression of fluids close to the freezing point may be problematic. When natural gas is being pumped, the development relating to the formation of gas hydrates results in considerable problems. Gas hydrates are inclusion compounds which are similar to ice and in which small gas molecules, for example noble gases and various natural gas components, are surrounded in a cage of water molecules. Hydrate formation must be expected even with small amounts of liquid water and at temperatures of, for example, 10° C. The major gas catastrophe in the year 1988 on the Norwegian North Sea drilling rig Piper Alpha was supposedly due to such hydrate formation. Considerable additional operation costs are also incurred in natural gas pumping as a result of gas hydrate deposits, since they are deposited in pipelines, blocking them.